Why shear angle is given to press tool?

Answer 1

Cutting shear is given to punch or the die that function to reduce the necessary cutting tonnage by reducing effective area of shear ie creating scissor action

for eg considering cutting paper with scissors we will start from one side and progres to other end but it press tool is moved perpendicular instantly have to contact whole sheet, when shear angle is given at the instant of contact only small line of contact is made, thus reducing force required for shearing.